Take a look at the two videos at Disney and More link. On one of them, you can hear Mrs. Potato Head's voice introducing him prior to the curtains opening. Her costumed character might be someplace among the audience, but it doesn't show her.
Apparently it's just for fun, for the time being anyway.
Originally Posted by ichigopara
Mrs. Potato head introduces him. The best part is before Mr. Potato head comes out everyone has to chant po-ta-to po-ta-to po-ta-to!
Thanks ichigopara. Po-ta-to! Po-ta-to! Po-ta-to!
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